We are primarily interested in the secretory absorptive and microbial digestive processes which occur in the large intestine. Therefore we are examining the rate of digesta passage as well as the composition of digesta in the gastrointestinal tract of a wide range mammalian and a few other vertebrate species, under controlled conditions of diet, dietary regime and at selected times after feeding. In addition, we are conducting studies of secretory and absorptive mechanisms in a limited number of selected species by in vivo perfusion and in vitro mucosal transport procedures. These comparative studies are used to look for structural-functional correlations.